Bacillus subtilis is a spore-forming probiotic bacterium that has been investigated for its effects on the gut-associated lymphoid tissue (GALT), of which Peyer’s patches are a central component. Peyer’s patches, found predominantly in the small intestine, play a vital role in initiating immune responses to gut antigens and maintaining intestinal homeostasis.

Several studies in animal models have shown that Bacillus subtilis supplementation can influence the immune system, including modulating the number and activity of cells in Peyer’s patches. For example, Hong et al. (2009) reported that B. subtilis spores could be taken up by Peyer’s patches, leading to immune stimulation and enhanced production of secretory IgA, an important antibody in mucosal immunity. Other research in poultry and rodents has demonstrated increased lymphocyte proliferation and improved gut immune barrier function after B. subtilis supplementation.

However, direct evidence in humans is limited, and the majority of data comes from in vitro studies or animal models. While there is a plausible scientific basis for its use to support the function of Peyer’s patches and the gut immune system, robust clinical trials in humans are lacking. Therefore, the evidence is preliminary and cannot be considered strong or definitive at this time.